High temperature cobalt-base and nickel-base superalloys are used in the manufacture of high temperature operating gas turbine engine components, including the nozzles, combustors, and turbine vanes and blades. During the operation of such components under strenuous high temperature conditions, various types of damage or deterioration can occur. For example, erosion and cracks tend to develop at the trailing edge of nozzles during service due to stresses that are aggravated by frequent thermal cycling. Over time, the severe operating conditions of the nozzles can develop cracks that measure up to one millimeter wide and fifty millimeters long. Because the cost of components formed from high temperature cobalt and nickel-base superalloys is relatively high, it is typically more desirable to repair these components than to replace them.
Repair methods for nozzles formed from superalloys specially adapted for their operating environment have included gas tungsten arc welding techniques. However, a more recent and cost effective approach that has been adopted for the repair of superalloy components is termed activated diffusion healing, or ADH, which involves a vacuum brazing operation. The ADH process employs an alloy powder or mixtures of powders that will melt at a lower temperature than the superalloy component to be repaired. If two powders are combined, one of the powders is formulated to melt at a much lower temperature than the other powder, such that upon melting a two-phase mixture is formed. The vacuum brazing cycle causes the braze powder mixture to melt and alloy together and with the superalloy of the component being repaired. A post-braze diffusion heat treatment cycle is then performed to promote further interdiffusion, which raises the remelt temperature of the braze mixture.
With the advent of higher strength and more highly alloyed superalloys, improved repair materials have been required that are specialized for the particular superalloy to be repaired. It is often the intent to provide a braze alloy that will result in a repair characterized by high strength and a microstructure that is closely matched with the microstructure of the article being repaired. As a result, a considerable variety of braze alloy materials have been developed for use in the ADH process and other braze repair techniques. While many highly suitable repair materials have been formulated to perform well with various high strength cobalt-base and nickel-base superalloys, the prior art lacks a braze repair material that is especially formulated to repair nozzles formed from certain superalloys. Of primary concern here, braze repair materials for nozzles must be uniquely tailored to the mechanical and environmental properties required for the particular nozzle to be repaired, whose property requirements will depend on the type of engine and its application, whether aerospace or industrial.